Nasal mask and mask cushion therefor

ABSTRACT

A nasal cushion ( 30 ) comprises a substantially triangularly shaped frame ( 32 ) from which extends a membrane ( 34 ). The frame ( 32 ) has a scalloped edge ( 36 ) by which the cushion ( 30 ) is affixed to a mask body. The membrane ( 34 ) has an aperture ( 38 ) into which the wearer&#39;s nose is received. The membrane ( 34 ) is spaced away from the rim ( 40 ) of the frame ( 32 ), and its outer surface ( 41 ) is of substantially the same shape as the rim ( 40 ). Respective notches ( 42,44 ) receive the bridge of the wearer&#39;s nose. The wearer&#39;s nose is received through the aperture ( 38 ) into the chamber within the mask body ( 46 ). The seal forming portion ( 45 ) thus contacts both the surface of the wearer&#39;s nose and a portion of the wearer&#39;s face in the region between the base of the nose and the upper lip, and around the sides and over the bridge of the nose. The shape of the seal forming portion ( 45 ) is particularly suited to effectively seal the difficult region of the facial contour that is the crease between the sides of the nose and the face.

RELATED APPLICATION

This application claims priority to Australian Provisional PatentApplication No. PO1265 filed Jul. 26, 1996, through PCT Application No.PCT/AU97/00450 filed Jul. 16, 1997. This application contains subjectmatter related to co-pending U.S. patent application Ser. No. 08/791,212filed Jan. 31, 1997, which also claims priority to AustralianProvisional Patent Application No. PO1265 filed Jul. 26, 1996.

FIELD OF THE INVENTION

The invention relates generally to a nasal mask and to a cushiontherefor, for example, for use in the treatment of respiratoryconditions and in assisted respiration.

BACKGROUND OF THE INVENTION

Nasal masks are commonly used in the treatment of respiratory conditionsand sleep disorders (e.g., obstructive sleep apnea) by delivering a flowof breathable gas for, or to assist patient respiration. These nasalmasks typically receive a gas supply line which delivers gas into achamber formed by walls of the mask. The walls usually are semi-rigidand have a face contacting portion including an aperture which isaligned with the wearer's nostrils. The face contacting portion cancomprise a soft, resilient elastomeric material which may conform tovarious facial contours. The mask normally is secured to the wearer'shead by straps. The straps are adjusted to pull the mask against theface with sufficient force to achieve a gas tight seal between the maskand the wearer's face. Gas is thus delivered to the mask and through theaperture to the wearer's nasal passages.

Problems often arise with masks of the above configuration. For example,the mask may be dislodged, thereby breaking the seal between the maskand wearer. This may occur if the wearer rolls over when sleepingthereby creating a drag force on the gas supply line which istransmitted to the mask, breaking the seal. In the case of a mask beingused for the administration of Continuous Positive Airway Pressure(CPAP) treatment for the condition obstructive sleep apnea, such a leakcan result in the pressure supplied to the entrance of the wearer'sairway being below the therapeutic value, and the treatment becomingineffective.

Another problem is that the face contacting portion may apply excessivepressure to the wearer's face resulting in discomfort and possibly skinirritation. This excessive forces. In some cases these excessivepressures and forces may cause the face to distort to conform with theface contacting portion to increase wearer discomfort, facial sorenessand ulceration.

Other types of devices exist whereby small nostril nosepieces (pillows)are held in place by a harness strapped over the wearer's head, forexample as shown in prior art U.S. Pat. No. 4,782,832. While thisarrangement may alleviate some problems regarding seal breakage and skinabrasion, the harnesses associated with such devices are quitecumbersome for the wearer, as are the gas supply lines. Also, air‘jetting’ into the nostrils can be irritating to the patient making suchdevices generally uncomfortable to use.

In FIGS. 1-3, a prior art nasal cushion 10, generally equivalent to thatshown in prior art U.S. Pat. No. 5,243,971, is first described.

As shown, the cushion 10 generally includes a base 11 from which dependsa semi-rigid cushion frame 12 formed of elastomeric material. Attachedover the outside of the frame 12 is a membrane 15, also of elastomericmaterial, having at its distal end a face contacting portion 14. Theframe 12 and the membrane 15 generally form a chamber 17 into which thewearer's nose can be received. The frame 12 bas a notch 19 toaccommodate the bridge of the wearer's nose. The base 11 includes slots13 to accommodate straps (not shown) to secure the cushion 10 and a maskbody (not shown) in combination to the wearer's head.

An aperture 16 is formed at the end of the membrane 15 distal from theframe 12 providing access for a wearer's nose 20 to the chamber 17 asnoted. As shown, the aperture 16 in an unflexed state is generallycircular (or elliptical) and is large enough to allow partial entry ofthe wearer's nose. The resilience of the membrane material allows theface contacting portion 14 and the aperture 16 to invert when the noseis received. The inverted membrane arrangement relies upon a positivepressure of supplied gas within the mask to effect a seal to thewearer's face. The seal is characterised as a “rolling edge seal”, inthat there can be motion of the cushion 10 relative to the patient'sface yet the seal is maintained. Even so, a tuck 22 arises in thevicinity of the upper lip due to the circular shape of the aperture, andit is from this tuck that leaks can arise to head and body movementduring sleep.

It is an object of the invention to overcome or at least substantiallyameliorate one or more of the foregoing disadvantages.

SUMMARY OF THE INVENTION

In one broad form, the invention discloses a nasal mask cushion tosealingly connect a mask to a wearer's face, the cushion comprising:

a substantially triangularly-shaped frame of resilient material having arim to surround the wearer's nose;

a membrane also of resilient material, the membrane being relativelymore flexible than the frame, and being of the same general shape assaid rim and fixed to and extending away from the frame so as to have anouter surface spaced from the rim, a portion of said outer surfaceforming a face contacting seal; and

a nose-receiving cavity bounded by said frame and said membrane;

and wherein said seal portion is generally coterminous with respect tosaid rim and is resiliently deformable towards the rim in use of thecushion.

Preferably, the rim and seal portion are shaped to generally matchfacial contours of the facial tissue around the sides and over thebridge of the nose and between the base of the nose and the top lip.

In one particularly advantageous form, the membrane is substantiallysaddle-shaped. The membrane further has a centrally located aperturethrough which the wearer's nose passes to enter said cavity.

It is preferred that the cushion and membrane each include a co-locatednotch to accommodate the bridge of the nose of the wearer. Typically,the seal portion contacts at least the wearer's nose, and preferably,also the facial tissue around the sides and over the bridge of the noseand between the base of the nose and the top lip.

The invention further discloses a nasal mask for connection to a wearers face comprising:

a mask body for connection with a supply of breathable gas; and

a nasal cushion, the body and cushion defining a nose-receiving cavity,the cushion including:

a substantially triangularly-shaped same of resilient material having arim to surround the wearer's nose;

a membrane also of resilient material, the membrane being relativelymore flexible than the frame, and being of the same general shape assaid rim and fixed to and extending away from the frame so as to have anouter surface spaced from the frame, a portion of said outer surfaceforming a face contacting seal;

and wherein said seal portion is generally coterminous with respect tosaid rim and is resiliently deformable towards the rim in use of themask.

The mask body can further include attachment points from which securingstraps can be attached, and by which the mask can be secured to thewearer's head. The nasal mask can yet further comprise an arm dependingfrom said body from which a further securing strap(s) can be attached.

The invention further discloses nasal CPAP treatment apparatuscomprising a flow generator for the supply of gas at a pressure elevatedabove atmospheric pressure to a gas delivery conduit, the conduit inturn coupled to a nasal mask as described immediately above.

In one particularly preferred form, a supply of gas can be provided tosaid cavity, said supply of gas assisting, but not solely causingmaintenance of a seal by said seal forming portion of said membrane tothe face of the wearer in use of the cushion.

Advantageously, because the membrane and the rim are substantiallyshaped to the facial contour, and the membrane does not need to turn inon itself, as in the prior art, thus contacting the face without foldsor creases. With the cushion/mask secured to the wearer's head, theheadstraps need only to be tensioned to balance the force due to maskgas pressure that tends to lift the mask off the face. Such relativelylower mask-to-face pressure results in greater patient comfort, and areduction in the likelihood of skin irritation.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described with reference tothe accompanying drawings, in which:

FIG. 1 is an exploded perspective view of a prior art nasal mask;

FIG. 2 is a perspective view of the prior art nasal mask of FIG. 1;

FIG. 3 is a perspective view of the prior art nasal mask attached to awearer;

FIG. 4 is a rear perspective view of a mask cushion embodying thepresent invention;

FIG. 5 is a cross-sectional view along line 5—5;

FIG. 6 is a perspective view of a nasal mask including the cushion ofFIGS. 4 and 5; and

FIG. 7 is a perspective view of the nasal mask of FIG. 6 secured to awearer's head.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 4 shows a perspective view of a nasal cushion 30 embodying theinvention. FIG. 5 shows the cross-sectional view along line 5—5. Thecushion 30 comprises a substantially triangularly shaped frame 32 fromwhich extends a membrane 34. The frame 32 has a scalloped edge 36 bywhich the cushion 30 is affixed to a mask body, as presently will bedescribed.

The membrane 34 has an aperture 38 into which the wearer's nose isreceived in use of the cushion 30. The membrane 34 is spaced away fromthe rim 40 of the frame 32, and its outer surface 41 is of substantiallythe same shape as the rim 40. The outer surface 41 of the membrane 34and the rim 40 of the frame 32 also can be described as generally saddleshaped. The shaping of the outer surface 41 of the membrane 34 and therim 40 of the frame 32 also include respective notches 42,44 thatreceive the bridge of the wearer's nose in use of the cushion 30.

As is best seen in FIG. 5, the frame 32 and the membrane 34 areintegrally formed, typically by in a one-shot molding process. The frame32 and the membrane 34 are fabricated from a resilient material. Onesuitable such material is Silastic™ silicone elastomer manufactured byDow Corning. The frame 32, in one preferred embodiment his a typicalthickness at its rim 40 of 1.5 mm. The membrane 34, in a preferredembodiment, has a typical thickness of 0.35 mm. In this way, themembrane 34 is relatively more flexible than the rim 40.

In use of the cushion 30, a wearer's nose will be inserted in theaperture 38 to engage a seal forming portion 45 (formed between thedashed lines) of the outer surface 41 to cause deformation of themembrane 34. Depending upon the securing force supplied to the membrane34, it may deform to a point where it butts against the rim 40 of theframe 32. The frame 32 has a rigidity sufficient to withstand usualsecuring pressures in use of the cushion 30 to tend to retain its shapeand resist deformation. It thus acts as a supporting structure.

Referring now to FIG. 6, the nasal cushion 30 is shown attached to amask body 46 by the edge 36 of the frame 32, adhered or otherwisesecured to a flange 48 of the mask body 46. Only the outer surface 41 ofthe membrane 34 can be seen. The flange 48 includes three slots 50-54from which tensioning straps can be attached to secure the cushion 30and the mask body 46 (in combination) to the head of a wearer.

The mask body 46 forms a cavity that can receive the nose of the wearerby the aperture 38. A port 56 is provided at the top of the mask body 46by which breathable gas can be supplied to the chamber.

Referring now to FIG. 7, there is shown a nasal mask 60 including themask body 46 and the mask cushion 30. A coupling tube 62 is connected atone end with the inlet port 56, and at the other to a socket 64 intowhich can be received a gas delivery tube (not shown) for the supply ofbreakable gas to the chamber internal of the mask body 46. The mask body46 also has two vent openings 66 by which expired gas is exhausted. Afirst fastening strap 68 is fixed between to the lower two slots 50,54.The upper slot 52 receives an arm 70, the top end of which has aresilient pad 72 to engage the forehead of the wearer. The arm 70 hastwo slots 74,76 along it side edges, by which a second fastening strap78 is secured.

In fitting the nasal mask 60, the wearer's nose is received through theaperture 38 into the chamber within the mask body 46. The seal formingportion 45 thus contacts both the surface of the wearer's nose and aportion of the wearer's face in the region between the base of the noseand the upper lip, and around the sides and over the bridge of the nose.The shape of the seal forming portion 45 is particularly suited toeffectively seal the difficult region of the facial contour that is thecrease between the sides of the nose and the face. Depending upon thetension applied by the fastening straps 68,78, a seal is formed with themembrane 34 remaining spaced from the rim 40 of the cushion frame 32.While the provision of pressurised gas to the chamber of the mask body46 assists in the maintenance of a seal between the membrane 34 and thewearer's nose and face, it is not essential in most cases, and aneffective seal will be formed absent any such pressurised gas. The sealformed between the membrane 34 and the wearer's nose and face is not inthe nature of a rolling seal in the manner of prior art as shown inFIGS. 1 to 3, as on relative movement of the mask 60 in relation to thewearer's head, the nose will be restrained by contacting the frame 32.Thus only limited relative motion between the mask 60 and the wearer'snose and face occurs.

The membrane 34 closely imitates the facial contour, and because of itsrelatively lesser stiffness than the frame 32, can conform to particularfacial structures with minimum force, and without a tendency to fold orcrease.

If the fastening strap 68,78 are tensioned to excess, the membrane 34deforms to abut the rim 40 of the cushion 32, the frame 32 thus actingas an “end lift”. In such a configuration, almost zero relative movementcan occur between the mask 60 and the wearer's head.

The nasal cushion 30 and nasal mask 60 has been described with referenceto CPAP or assisted respiration treatment, however it is to beunderstood that the invention generally is applicable to any applicationwhere gas and/or atomised liquid is to be supplied to the entrance ofthe nasal airways. Such applications include nebulisers, gas masks andanaesthetic machines.

What is claimed is:
 1. A nasal mask cushion assembly to sealinglyconnect a nasal mask to a wearer's face by adjusting tension on at leastone tension strap connected to the nasal mask, the cushion assemblycomprising: a generally triangularly shaped frame of resilient material,the frame including an inner surface, an outer surface, an aperture, anda rim defining the perimeter of the aperture, the rim including a notchin a region of the rim adapted to receive the bridge of the wearer'snose; and a generally triangularly shaped membrane of resilientmaterial, the membrane including an aperture adapted to receive thewearer's nose, an outer surface including a seal forming portion adaptedto deform and form a seal over a portion of the wearer's face in aregion between the base of the nose and the upper lip and around thesides and over the bridge of the wearer's nose when the mask is in use,an inner surface opposing the outer surface of the frame and spaced afirst distance from the outer surface of the frame in at least theregion of the frame adapted to receive the bridge of the wearer's nosewhen the mask is in use, an edge defining the perimeter of the aperture,and a notch in a region of the membrane adapted to receive the bridge ofthe wearer's nose, wherein the membrane is more flexible than the frame;the aperture of the frame is larger than the aperture of the membrane;the edge of the membrane is spaced a second distance from the rim, thesecond distance being variable and largest in the regions of the rim andthe membrane adapted to receive the bridge of the wearer's nose; and thefirst distance between the outer surface of the frame and the innersurface of the membrane is variable with the tension applied to the atleast one tension strap.
 2. A nasal mask cushion assembly according toclaim 1, wherein the frame and the membrane are formed in a singlepiece.
 3. A nasal mask cushion assembly to sealingly connect a nasalmask to a wearer's face by adjusting tension on at least one tensionstrap connected to the nasal mask, the cushion assembly comprising: agenerally triangularly shaped frame of resilient material, the frameincluding a first side adapted to contact a mask body of the nasal mask,a second side opposite the first side, an aperture extending from thefirst side to the second side, a rim on the second side extending aroundthe perimeter of the aperture, and a notch in the rim in a regionadapted to receive the bridge of the wearer's nose; and a generallytriangularly shaped membrane of resilient material, the membraneincluding an aperture adapted to receive the wearer's nose, an edgedefining the perimeter of the aperture, a notch in a region adapted toreceive the bridge of the wearer's nose, a first surface including aseal forming portion disposed around the perimeter of the apertureadapted to deform and form a seal over a portion of the wearer's face ina region between the base of the nose and the upper lip and around thesides and over the bridge of the wearer's nose when the mask is in use,a second surface opposite the first surface that surrounds and is spaceda first distance from the rim of the frame in at least the regionadapted to receive the bridge of the wearer's nose when the mask is inuse, wherein the membrane is more flexible than the frame; the apertureof the membrane is smaller than the aperture of the frame; the edge ofthe membrane is spaced a second distance from the rim of the frame, thesecond distance being variable and largest in the regions of themembrane and the frame adapted to receive the bridge of the wearer'snose; the first distance between the second surface of the membrane andthe rim of the frame is variable with the tension applied to the atleast one tension strap.
 4. A nasal mask cushion assembly according toclaim 2, wherein the frame and the membrane are formed in a singlepiece.